## 
## File		: timeQueue.py 
## 
## Author       : Chris Miles - http://chrismiles.info/
## 
## Start Date	: 20001005
## 
## Description	: Queue-derived queue ordering objects by next-run time.
##
## $Id: timeQueue.py 706 2005-06-29 08:58:16Z chris $
##
##
########################################################################
## (C) Chris Miles 2001-2005
##
## The author accepts no responsibility for the use of this software and
## provides it on an ``as is'' basis without express or implied warranty.
##
## Redistribution and use in source and binary forms are permitted
## provided that this notice is preserved and due credit is given
## to the original author and the contributors.
##
## This program is distributed in the hope that it will be useful,
## but WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
########################################################################

"""
timeQueue is the queueing class derived from Python's Queue class.  It is as
thread-friendly as Queue, the major difference being objects are inserted
into the queue based on a given time.  Objects with the lowest times are
closest to the front of the queue.

To support this, objects have to be added along with their time, so a 
2-tuple must be added, eg: q.put( (obj, time) ).  Similarly q.get()
returns the same 2-tuple.

An extra public method has been added, over what Queue offers, q.head().
This method returns the item (and time) from the front of the queue,
exactly as q.get(), but does not remove it from the queue.

doctests:

>>> q = timeQueue(0)
>>> q.put( ('a',0) )
>>> q.head()
('a', 0)
>>> q.get(block=0)
('a', 0)
>>> q.get(block=0)
Traceback (most recent call last):
    ...
Empty
"""


# Imports: Python
import Queue


class timeQueue(Queue.Queue):
    """We only need to override the methods below to implement
    our own type of queue.  The parent Queue class handles the rest.
    These will only be called with appropriate locks held."""

    def head(self, block=1, timeout=None):
	"""Return the head item in the queue without removing it from
	the queue. (get() will remove item from queue.)

        If optional arg 'block' is 1 (the default), block if
        necessary until an item is available.  Otherwise (block is 0),
        return an item if one is immediately available, else raise the
        Empty exception."""

	if 'not_empty' in dir(self):
	    # Python 2.4+ Queue implementation...
	    self.not_empty.acquire()
	    try:
		if not block:
		    if self._empty():
			raise Empty
		elif timeout is None:
		    while self._empty():
			self.not_empty.wait()
		else:
		    if timeout < 0:
			raise ValueError("'timeout' must be a positive number")
		    endtime = _time() + timeout
		    while self._empty():
			remaining = endtime - _time()
			if remaining <= 0.0:
			    raise Empty
			self.not_empty.wait(remaining)
		item = self._head()
		self.not_full.notify()
		return item
	    finally:
		self.not_empty.release()

	else:
	    # Pre-Python 2.4 Queue
	    if block:
		self.esema.acquire()
	    elif not self.esema.acquire(0):
		raise Empty
	    self.mutex.acquire()
	    was_full = self._full()
	    item = self._head()
	    if was_full:
		self.fsema.release()
	    if not self._empty():
		self.esema.release()
	    self.mutex.release()

	return item


    # Initialize the queue representation
    def _init(self, maxsize):
        self.maxsize = maxsize
        self.time_queue = []	# queue in order of time
        self.object_list = []	# list of objects to return

    def _qsize(self):
        return len(self.time_queue)

    # Check wheter the queue is empty
    def _empty(self):
        return not self.time_queue

    # Check whether the queue is full
    def _full(self):
        return self.maxsize > 0 and len(self.time_queue) == self.maxsize

    # Put a new item in the queue
    def _put(self, it):
	(item, time) = it
	if self._empty():
	    # queue is empty, add to start
	    self.time_queue.append(time)
	    self.object_list.append(item)
	else:
	    i = 0
	    while i < len(self.time_queue):
		if time < self.time_queue[i]:
		    self.time_queue.insert(i, time)
		    self.object_list.insert(i, item)
		    break
		i = i + 1
	    if i == len(self.time_queue):
		# append to end
		self.time_queue.append(time)
		self.object_list.append(item)

    # Get an item from the queue
    # We always want the first item from queue
    def _get(self):
        time = self.time_queue[0]
        item = self.object_list[0]
        del self.time_queue[0]
        del self.object_list[0]
        return (item,time)

    # Get item from the top of the queue but do not remove it
    def _head(self):
        time = self.time_queue[0]
        item = self.object_list[0]
        return (item,time)


## doctest:
def _test():
    import doctest
    doctest.testmod()

if __name__ == "__main__":
    _test()

##
## END - timeQueue.py
##
